GUESTS for the upcoming wedding of Prince Harry and Meghan Markle could be vetted by police amid a potential stalking threat that could pose a security risk on May 19.

That’s according to former royal aide and security expert Alex Bomberg who said all those invited inside the castle will undergo checks “to some level or another” as police cover all bases in the final weeks leading up to the royal nuptials in Windsor.

The close protection specialist who runs a company providing specialist security around the world said there was a huge range of security issues to be dealt with behind the scenes from obsessive stalkers to threats on social media and those who want to create chaos in the large crowds.

He said terrorists would look to attack the “weakest possible location” on the day.

“Historically members of the royal family and obviously major celebrities such as Meghan have always suffered problems with stalking,” he said. “Police will be keeping an eye on that, looking for any potential threats which may evolve via social media … and they’ll be acting upon those threats.”

Royals and celebrities have both been magnets for stalkers in the past. Picture: Eddie Mulholland/Pool via APSource:AP

The chapel is inside castle walls but the couple will take a carriage ride through the city. Picture: Thames Valley PoliceSource:Supplied

Police also fear the couple’s open top carriage ride through the city could pose “major security problems” with the narrow cobbled streets and tall buildings creating an atmosphere that could be turned into “downtown Sarajevo” where snipers targeted civilians, The Sunday Times reports.

Mr Bomberg said the couple will be briefed on emergency plans for the day and will “know exactly what to do if anything does happen,” as a result of intense security briefings and close protection officers working around them.

“They will certainly be very, very aware of the security operation going on. This is a couple on their wedding day so they’ve got this to have in the back of their minds as well.”

“I can’t see them getting attacked personally but the odds of there being an incident involving the crowd is obviously a lot higher. Terrorists will look to attack the weakest possible location so that’s what the concerns are,” he said.

The castle grounds. Picture: Thames Valley PoliceSource:Supplied

Manholes and drains are expected to be sealed by police, with 100,000 people expected to pour into the city. Picture: Thames Valley PoliceSource:Supplied

The royal wedding has sparked the largest security operation in Thames Valley Police history and is expected to draw more than 100,000 people to the medieval city made up of narrow cobbled streets and a hilltop castle where the service will take place.

Police have already announced a “ring of steel” to surround the area with automatic numberplate recognition technology, CCTV and barriers to prevent cars crashing into crowds already deployed. The force has also reportedly bought a “net of spikes” that can stop a vehicle in less than a minute, the Evening Standard reports.

It comes as police are already investigating a letter containing white powder sent to Ms Markle earlier this year that is being treated as a “racist hate crime”. Ms Markle has already reportedly been assigned 24-hour protection despite not yet becoming a full-time royal.

Prince Harry was forced to reveal their relationship in November 2016 following a wave of “fictional stories” about his then-girlfriend, saying she was subject to “outright sexism and racism of social media trolls”.

The city has already gone crazy for the royal wedding. Picture: AFP/Tolga AkmenSource:AFP

The carriage Meghan and Prince Harry use might have more gold on it than this one. Picture: AFP/Tolga AkmenSource:AFP

On the day, the couple will wed at St George’s Chapel which is inside castle grounds and not accessible to the public. However they have invited in more than 2000 people from local charities and schools and will take a carriage ride on a predetermined route to interact with crowds.

While the Queen’s country estate is no stranger to state visits and celebrations, having hosted her 90th birthday and the Obamas in the past, Mr Bomberg said the unique venue provides a range of challenges that teams working at the 2011 wedding between the Duke and Duchess of Cambridge did not have to contend with.

“Central London and The Mall is a very easy place to police, it’s a very wide area. It’s not overlooked by buildings. Here we’re in the middle of a medieval town, so it’s very difficult here, you’ve got lots of turns, lots of tight turns for carriages to make and I think it will be quite difficult for police to manage in the small areas.”

Those arriving in the city on the day can expect to be searched, while bins, drains and manholes will be sealed prior to the event and at some point it will be blocked off to become “sterile”, Mr Bomberg said.

Police said they intend to use local business owners as their “eyes and ears” and are encouraging the public to report anything that seems suspicious.